We have produced and characterized SHIV virus-like particles (VLPs) containing SIV Gag and HIV envelope (Env) proteins by using a baculovirus expression system. Recombinant SIV Gag (SIVmac239) and full length or truncated HIV Env from either HIV BH10 or HIV 89.6 viruses were coexpressed in insect cells and the envelope incorporation into SHIV VLPs was characterized. The expression level of the Env protein was found to be about 20% to 50% higher in the cytoplasmic domain truncated Env of both strains. Cell surface expression of truncated Env protein was found to be 8 fold higher than full-length Env protein. Furthermore, the truncated Env exhibited higher cleavage property to produce biologically active gp120 than the full-length Env. Production of SHIV VLPs in serum media helped produce cleaved Env protein in both full length and truncated Env VLPs. Coinfection of a recombinant virus expressing the protease furin also resulted in more efficient cleavage from t he Env pr ecursor to gp120. SHIV VLPs produced from coexpression of SIV Gag and HIV truncated Env have more Env incorporation than coexpression with full length Env detected in both Western blot and ELISA test. Both full length and truncated Env were found to be transported to the cell surface and to induce CD4+ cell fusion. Immunoelectron microscopic analysis of VLPs displayed the incorporation of both full length and truncated Env on the surfaces of VLPs. These results indicate that the truncated Env exhibits more efficient cleavage and assembly than full-length Env in SHIV VLPs. Studies of immunogenicity of full length and truncated Env SHIV VLPs and optimum usage of adjuvant in the immunization in animal model are in progress. FUNDING NIH / NIAID $100,000 08/01/98 - 03/31/03 PUBLICATIONS None P51RR00165-38 1/1/1998 - 12/31/1998 Yerkes Regional Primate Research Center